The invention comprises a method and apparatus for generating a multi-carrier high definition television (HDTV) signal including a digital sound and sync (DSS) signal. The invention incorporates baseband and RF processing necessary to reduce the bandwidth of an HDTV source signal to that of a conventional television signal, for example 6 MHz at RF. The inventive signal format will be referred to herein as "HDS/NA-6". The baseband HDTV source signal may be 525 lines, 1:1 progressive scanning or 1050 lines, 2:1 interlaced scanning.
Any system for transmitting HDTV will have to initially co-exist with conventional television receivers. Proposed systems to provide such compatibility fall mainly into two categories: "augmentation" systems and "simulcast" systems. Both of these systems seek to take maximum advantage of the existing broadcasting spectrum and at the same time provide both HDTV service for appropriately equipped receivers, and conventional television broadcast service, for example NTSC, for existing television receivers.
U.S. Pat. No. 4,694,338 cited above, as well as pending applications for example, U.S. patent application Ser. Nos. 239,096; 239,091; and 239,148, all filed on Aug. 31, 1988 and owned by the present assignee, relate to methods for providing an HDTV transmission system using the "augmentation" methodology. In such "augmentation" systems, a conventional television signal is transmitted on one conventional television channel. On an adjacent channel, which can be a so-called "taboo" channel, an "augmentation" signal is transmitted which, when combined with the conventional signal in an appropriate receiver, will provide an HDTV display.
The so called "simulcast" systems for providing compatible HDTV service utilize one conventional television channel to transmit a non-compatible HDTV television signal and an adjacent television channel to transmit a conventional television signal which can provide the same programming ("simulcast") as the HDTV signal. Although this method requires the use of two conventional television channels to provide one "compatible" program (HDTV and conventional versions), the degree to which programs are "simulcast" will probably diminish as the number of HDTV receivers increases in proportion to the total number of receivers. The television spectrum therefore can be gradually converted to HDTV signals as conventional television receivers are replaced with HDTV receivers. Although proposals have been made for such "simulcast" systems, for example the Zenith "Spectrum" system and the NHK "MUSE-6" system, up to now, a practical and efficient system for placing a true HDTV signal (one having for example a 16:9 aspect ratio, a horizontal resolution of about 500 TVL/ph and a vertical resolution of about 680 TVL/ph, with minimal motion artifacts) on a conventional broadcast, cable or recording channel did not exist. An object of the instant invention is to provide such a system.
It is another object of the invention to provide a system for transmitting an HDTV signal which can evolve naturally and economically from the existing conventional broadcasting standards.